Causes and consequences of material variation in avian nest building

Houses around the world are built with a variety of materials like timber and brick, depending on a number of factors such as local climate and material availability. Similarly, non-human animals such as birds use diverse materials to build nests. Very little is known about how animals choose nest materials, and how these choices, in turn, affect the function of the nests they build. As an initial attempt to address this question, we investigated the causes and consequences of nest-material use by Dartford warblers (Sylvia undata). The warblers breeding in England show considerable variation in nest materials: some nests are made almost entirely of heather, while others contain a lot of grass. We found that the warblers’ use of nest materials were explained by the composition of the local habitats, but no evidence for relationships between nest-material composition and insulation capacity or the breeding performance. Warblers appear to be able to build equally functional nests using whatever materials are readily available in respective habitats. Studying nest-building behaviour of individual species like Dartford warblers could inform how the use of diverse material in animal architecture evolved.